Road navigation systems are systems for assisting the driving and guiding of landborne vehicles that allow an itinerary between a departure point and an arrival point specified by the driver and/or the current position of the vehicle to be calculated, and the itinerary to be presented, by means of a scroll-down display, for example, for use in a more or less interactive manner.
For this purpose, the navigation system accesses a mapping database that groups all of the road segments, and the itinerary is calculated by linking the road segments between the departure and arrival points.
This procedure is capable of generating numerous itineraries.
A supplementary function, which allows a particular route to be determined as a function of the preferences of the driver, is generally added.
For example, he may select the itinerary exhibiting the shortest distance between the departure and arrival points, but he may also select the itinerary allowing these two points to be connected as quickly as possible. These two itineraries may be identical, or completely or partially different. The driver may also indicate whether or not he wishes to use motorway segments or, conversely, avoid all of the corresponding toll charges.
There are currently three types of navigation system.
The first type, known as an on-board system, is an autonomous system installed on board a vehicle and having its own mapping, generally stored on an optical storage medium such as a CD ROM or DVD ROM.
The second type, known as a hybrid system, is a system in which part of the information (in particular the ground mapping) is placed in a remote server and part of the ground mapping, that assisting the itinerary once it has been calculated, is downloaded into the terminal, which will use it in the manner of an on-board system.
The third type, known as an off-board system, is a system in which all of the processing is carried out in a remote server. The on-board terminal in the vehicle serves merely to return the GPS location information to the server, then to restore the indications issuing from the server, in particular the guidance commands. The communication between the server and the on-board terminal is conducted via cellular telecommunication networks.
In an off-board navigation system, of the third type, the itinerary is calculated and stored in the server. Said server scrolls through and displays this itinerary and provides the terminal with the guidance information as a function of the position information that it receives from the GPS positioning module of said terminal.
Current off-board navigation systems rely on cellular telephony communication networks in order to exchange information between the server and the on-board terminal in a vehicle.
None of the aforementioned navigation systems allows for the transmission periods that are inherent to the transmission system used. Latency times, which are defined as the periods between the emission of an item of information and the receipt thereof, are quite simply ignored.
The aim of the present invention is to overcome the aforementioned drawbacks of the off-board navigation systems of the prior art.
In particular, one aim of the present invention is to take into account, in an adaptive manner, the latency periods of the transmission network used by the off-board navigation systems of the prior art, in order to improve their mode of operation and reliability independently of the characteristics or the speed of the vehicle.
A further aim of the present invention is also to implement a method and a vehicle-external navigation server allowing an on-board terminal on a vehicle having an off-board navigation system to be provided with guidance information corresponding substantially to the location of the vehicle and the on-board system thereon at the moment when they receive this guidance information, and not to their previous location at the moment when the on-board positioning module on this vehicle sent its geographical position.